The Fostex T50RP MK3 is 50Ω at 92.0 dB/mW; the HiFiMAN Susvara is 60Ω at 83.0 dB (no reference unit printed). This page is only about what they ask of an amplifier — not how they sound, which no specification on either sheet can tell you.
The HiFiMAN Susvara needs 9.0 dB more than the Fostex T50RP MK3 to reach the same loudness — 50 mW against 6.3 mW.
| Specification | Fostex T50RP MK3 | HiFiMAN Susvara |
|---|---|---|
| Impedance | 50 Ω | 60 Ω |
| Sensitivity | 92.0 dB/mW | 83.0 dB |
| Sensitivity (voltage) | 105.0 dB/V | 95.2 dB/V |
| Power for 100 dB | 6.3 mW | 50 mW |
| Voltage for 100 dB | 0.56 V | 1.73 V |
| Current for 100 dB | 11.2 mA | 28.9 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 6.25 Ω | 7.50 Ω |
| Sources that reach 100 dB out of 280 | 280 | 231 |
One caution before reading the rows. HiFiMAN Susvara printed a decibel figure with no reference unit, so this page reads it as per milliwatt. If it is really per volt, that model needs far more than the table says. Why the two readings differ by so much.
49 of the 280 sources have the power for the Fostex T50RP MK3 but not for the HiFiMAN Susvara — Apple USB-C dongle (US), Apple USB-C dongle (EU), Generic CX31993 dongles, 46 more.
231 of the 280 sources here reach 100 dB on both. That count is about power only — the output-impedance and hiss lines above are separate questions, and a source can pass this one and fail those.
Each model has a page of its own with the full source list, the hiss estimate and the provenance of every figure above: Fostex T50RP MK3 and HiFiMAN Susvara. Each figure on this page is labelled on those pages with where it came from, including the ones Fostex and HiFiMAN never published — what Fostex publishes and what HiFiMAN publishes, both counted.